FIGS. 3(a) and 3(b) show a circuit construction of a prior art attenuator and its input and output waveforms. FIG. 3(a) is circuit diagram of the attenuator, and FIG. 3(b) is a diagram illustrating the output waveforms against its input signal. In FIG. 3(a), a signal applied to an input terminal V.sub.IN is divided by a dividing circuit of resistors R.sub.01, R.sub.12, R.sub.23, R.sub.34, R.sub.45 and R.sub.5G which are serially connected to each other between the input terminal V.sub.IN and the ground. This divided signal is obtained from an output terminal V.sub.OUT by turning on one of the switches of a switch SW.sub.0 connected between the input terminal V.sub.IN and the output terminal V.sub.OUT, a switch SW.sub.1 connected between the resistors R.sub.01 and R.sub.12 at its one end and connected to the output terminal V.sub.OUT at the other end, a switch SW.sub.2 connected between the resistors R.sub.12 and R.sub.23 at its one end and connected to the output terminal V.sub.OUT at the other end, a switch SW.sub.3 connected between the resistors R.sub.23 and R.sub.34 at its one end and connected to the output terminal V.sub.OUT at the other end, a switch SW.sub.4 connected between the resistors R.sub.34 and R.sub.45 at its one end and connected to the output terminal V.sub.OUT at the other end, and a switch SW.sub.5 connected between the resistors R.sub.45 and R.sub.5G at its one end and connected to the output terminal V.sub.OUT at the other end. Reference character C designates a load capacitance between the output terminal V.sub.OUT and the ground potential.
A description is given of the operation.
Suppose that a signal V.sub.i input to the input terminal V.sub.IN is a sinusoidal wave of angular frequency .omega. and wave height, i.e., amplitude, V.sub.0. This signal V.sub.i is divided by the serially connected resistors R.sub.01, R.sub.12, R.sub.23, R.sub.34, R.sub.45 and R.sub.5G, and for example, the divided voltage V.sub.1 appearing at a node between the resistors R.sub.12 and R.sub.23 of a wave height V.sub.1 is represented by the following formula (1): ##EQU1## Thereupon, when only the switch SW.sub.2 is turned on, an output signal V.sub.o of wave height V.sub.1 shown in the formula (1) is output to the output terminal V.sub.OUT.
Similarly, the divided voltage V.sub.2 appearing at a node between the resistors R.sub.45 and R.sub.5G of a wave height V.sub.2 is represented by the following formula (2): ##EQU2## Thereupon, when only the switch SW.sub.5 is turned on in place of the switch SW.sub.2, the output signal V.sub.0 of the wave height V.sub.2 as shown in the formula (2) is output to the output terminal V.sub.OUT with its angular frequency .omega..sub.0.
When the wave height of the input signal is V.sub.0, the angular frequency thereof is .omega., and the phase delay thereof is .omega..multidot.t.sub.0, the input signal V.sub.i is represented by the following formula (3): EQU V.sub.i =V.sub.0 .multidot.sin .omega.(t-t.sub.0) (3)
And when the wave height of the output signal is V.sub.m, the angular frequency thereof is .omega., and the phase delay thereof is .omega..multidot.t.sub.d, the input signal V.sub.o is represented by the following formula (4): EQU V.sub.0 =V.sub.m .multidot.sin .omega.(t-t.sub.d) (4)
FIG. 3(b) shows waveforms of the input signal V.sub.i and the output signal V.sub.o. In the output waveform, when only the switch SW.sub.2 is turned on, the wave height V.sub.m becomes V.sub.1 given by the formula (1), and the delay time t.sub.d becomes (t.sub.0 +t.sub.1), and the formula (4) becomes the following formula (5): EQU V.sub.0 (SW.sub.2)=V.sub.1 .multidot.sin .omega.(t-t.sub.0 -t.sub.1)(5)
In addition, when only the switch SW.sub.5 is turned on, the wave height V.sub.m becomes V.sub.2 as given by the formula (2), and the delay time t.sub.d becomes (t.sub.0 +t.sub.2), and the formula (5) becomes the following formula (6): EQU V.sub.0 (SW.sub.5)=V.sub.2 .multidot.sin .omega.(t-t.sub.0 -t.sub.2)(6)
The prior art attenuator is constructed as described above, and there arises a deviation in phase dependent on the degree of attenuation, and also it was difficult to control the phase of the output signal so as to compensate the deviation in phase.